Blood pressure measurement in the coronary artery is most commonly performed using a fluid filled catheter that transfers the pressure to a external pressure sensor or by a catheter based pressure sensor inside the artery. By measuring the pressure with a miniature sensor inside the artery the time response as well as the accuracy can be improved. The miniature sensor based measurement is well suited for use in balloon angioplasty procedures.
Pressure sensors intended for use in medical catheter based intravascular applications needs to be ultra miniaturized. To achieve a reliable measurement in the blood vessels the pressure sensors also needs to have a built in pressure reference. Vacuum or a low pressure is preferred to minimize temperature drift. Several techniques using MEMS technology have been proposed with optical reflective and interferometric, capacitive and piezoresistive detection. Piezoresistive detection technique is more favorable than capacitive detection for miniaturized sensors due to better scaling characteristic. An earlier reported absolute pressure sensor uses a piezoresistive strain gauge provided on top of a pressure deflectable diaphragm.
A successfully commercialized ultraminiaturized absolute pressure sensor is using the piezoresistive detection technique. The sensor accomplishes a leverage effect by separating the strain-gauge from the diaphragm with an insulation layer to obtain an increase of the sensitivity. However, the thickness of such an insulator also stiffens the diaphragm, thus reducing the sensitivity.